Sources

Game and Story Use

These can be difficult to pull off in a game, since unlike the writer of a story, the game master cannot predict what the player characters will do. And if the characters decide to fight fate, attempts to get them "back on track" can become railroading. But it can be very satisfactory when it is done right.

The trick, as all the best prophets throughout history knew - is to keep prophecies vague and allow for multiple interpretations. Thus, when a character does something that is very obviously his choice, you can ret con your backstory so that it fits the prophecy, and allow the character to find about the connection afterwards. As long as the players can't prove the ret con, you should be fine.